1. Field of the Invention
The present invention relates to a backlight unit and a head-up display device.
2. Description of the Related Art
Conventionally, there has been a head-up display device including a backlight. For example, Japanese Patent Application Laid-open No. 2007-108429 discloses a technology of a display device provided with a display part that displays desired information by being transmissively illuminated; a light source that is disposed at the rear of the display part and that transmissively illuminates the display part; a diffusion plate that uniformizes the light emitted from the light source; and a first condensing lens that condenses the light made uniform by the diffusion plate on the display part, and that transmissively illuminates the display part. It is described that the display device disclosed in Japanese Patent Application Laid-open No. 2007-108429 can reduce luminance unevenness of transmitted illumination light by the diffusion plate, while preventing a luminance reduction in the transmitted illumination light by the first condensing lens.
It is possible to improve luminance of an image by concentrating projection light on a certain range, by condensing the light from a light source using a condensing lens. On the other hand, when an eye point is changed due to a change of posture of the driver or the like, luminance of an image to be viewed may be varied.